THE SENSES 



553 



Mott points out that the conjugate movement of head and 

 eyes in following a moving object assists the judgment in forming 

 an idea of the rate of movement. In animals with panoramic 

 or semi-panoramic vision, the visual range is increased by move- 

 ments of the head rather than the eye. Steiner, quoted by Mott, 

 showed that in the young animal the motor cortex of the cere- 

 brum responds to excitation before the visual cortex ; in the 

 rabbit the motor is excitable on the ninth or tenth day, the 

 visual not until the fourteenth, and not until the fifteenth day 

 does the animal attempt flight if pursued. The dog is later ; 



Fig. 170. — Diagram showing 

 through both eyeballs, 

 Retina of the Horse. 



Horizontal Section of the Head passing 

 to illustrate corresponding points in the 



x, The frontal bones ; p p, portion of malar bone entering into the formation 

 of the outer rim of the orbit ; s, the nasal septum. Rays of light proceeding 

 from A are seen by both eyes, being imprinted on the temporal side of each 

 retina at a ; rays from B are seen at b in the left eye, but are not seen with 

 the right eye ; in the same way rays from C are imprinted at c in the left eye, 

 but cannot be seen with the right eye. 



the eyes are opened on the fourteenth day, but it is not until 

 the thirty-fourth that a dog avoids obstacles. He can see 

 directly to his front, but an object projected laterally on the 

 visual field is not looked for by head and eye movements. 

 Mott points out that visual images alone do not convey to the 

 mind the reality of the external world, unless associated with 

 locomotion and previous tactile and kinesthetic impressions, 

 which appear necessary factors before visual impression can 

 be translated and their meaning known. How true this is 

 will occur to all connected with the care and management 



